MRM has distinct advantages for defining chemical and functional microanatomy of organisms such as the barnacle which have both mineral and non-mineral components: it is nondestructive and three dimensional; tissue, and more importantly, mineral, do not have to be physically sectioned to be viewed from all angles. Maturation in these crustaceans involves changes in water content, tissue integrity, and calcium metabolism1, all of which are reflected in MRI "proton stain" contrast, based on water content, mobility and binding. MRM affording greater than 100 fm resolution imaging should enable documentation of this dynamic time course of changes in body and exoskeleton.2 The initial objective of this project has been to obtain optimum 3-dimensional MR images of the internal and external structures of the adult barnacle. The long term objective is to understand the mechanisms underlying biomineralization during its life cycle.